netdev - XDP applications running in driver mode on mlx5_core can't access various helper functions

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Date:   Thu, 15 Jul 2021 13:59:32 +0000
From:   David Ramirez <davramir@....edu>
To:     Saeed Mahameed <saeedm@...dia.com>,
        Leon Romanovsky <leonro@...dia.com>
CC:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-rdma@...r.kernel.org" <linux-rdma@...r.kernel.org>
Subject: XDP applications running in driver mode on mlx5_core can't access
 various helper functions

Hey all,

I am having issues with calling some bpf helper functions
when running my XDP program in driver on the mlx5_core driver.
Several of the helpers I've tried to use for ringbuf and maps always return 0.
While this may seem to imply that for functions that merely return null instead of
a pointer in case of an error are working as intended,
some functions which return negative on failure and 0 on success are are also affected,
as while they return 0, they do not result in the desired effect.

Observed examples:
 - bpf_ringbuf_output always returns 0, but no data is pushed to the ringbuf
 - bpf_map_update_elem always returns 0, but the element is not updated
 - bpf_ringbuf_reserve always returns 0
 - bpf_map_lookup_elem always returns 0

I'm uncertain if this is a driver specific issue or an ebpf issue.
Testing with xdp in driver mode on veth devices works as expected,
which suggests this is more likely a driver issue.

Additional Details:

Linux Distro: Ubuntu 21.04
Linux Kernel version: 5.11.0-18-generic
driver: mlx5_core
version: 5.11.0-18-generic

Thank you,
David Ramirez